Strong’s Dictionary of Greek Words:

diminutive from a derivative of the base of 5597; a crumb or morsel (as if rubbed off), i.e. a mouthful
KJV Usage:

From Manners and Customs of the Bible:

It was customary for the host to give to such of his guests as he chose a “sop,” or thin piece of bread dipped into the food in the dish, and saturated with its fluid part. See note on Mark 14:2020And he answered and said unto them, It is one of the twelve, that dippeth with me in the dish. (Mark 14:20) (#746). Jowett, in speaking of an entertainment at which he was a guest, says: “When the master of the house found in the dish any dainty morsel, he took it out with his fingers and applied it to my mouth” (Researches, p. 210).
This verse is of interest, since, taken in connection with the twenty-third verse, (see note preceding,) it indicates the position of Judas at the feast. He must have been very near to Jesus since he was within reach of his hand. He was very probably next to him; and since John lay to the right of the Saviour, Judas in all probability was at his left. If so, the Saviour must at times have laid his head on the traitor’s breast; and thus the base treachery of Judas is seen in a most revolting aspect. While the Master was pillowing his head upon him he was meditating on the chances of securing the blood-money for which he had contracted to betray his Lord!